Fair Value (Details)	1 Months Ended			12 Months Ended
	Jun. 30, 2017 USD ($)	May 31, 2017 USD ($) community	Apr. 30, 2017 USD ($)	Dec. 31, 2017 USD ($) community derivative venture	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Derivative instruments and Hedging Activities
Derivative Instruments, Gain (Loss) Reclassification from Accumulated OCI to Income, Estimated Net Amount to be Transferred				$ 376,000
Number of Real Estate Properties | community				267
Gain on Fair Value Hedge Ineffectiveness				$ 753,000
Amortization Period of Deferred Gain (Loss) on Discontinuation of Interest Rate Fair Value Hedge				10 years
Derivative, Notional Amounts Settled During Period	$ 214,900,000	$ 400,000,000	$ 185,100,000	$ 800,000,000
Receipts (payments) for termination of forward interest rate swaps	$ (4,078,000)	$ 1,361,000	$ 2,326,000	(391,000)	$ 14,847,000	$ 0
Income (loss) on cash flow hedges				$ (13,979,000)	$ (5,556,000)	$ 5,354,000
Cash Flow Hedges Interest Rate Caps
Derivative instruments and Hedging Activities
Number of derivative instruments held | derivative				7
Puts
Derivative instruments and Hedging Activities
Number of ventures in which entity is required to purchase interest in investment at guaranteed minimum amount | venture				3
Interest Rate Caps | Cash Flow Hedges Interest Rate Caps
Derivative instruments and Hedging Activities
Notional balance				$ 35,039,000
Weighted average interest rate (as a percent)				3.50%
Weighted average capped interest rate (as a percent)				5.90%
Interest Rate Swap [Member] | Cash Flow Hedges Interest Rate Caps
Derivative instruments and Hedging Activities
Notional balance				$ 300,000,000
Weighted average capped interest rate (as a percent)				2.40%
Derivative, Notional Amounts Entered into During Period				$ 300,000,000
Non-designated Hedges Interest Rate Caps
Derivative instruments and Hedging Activities
Number of derivative instruments held | derivative				14
Non-designated Hedges Interest Rate Caps | Interest Rate Caps
Derivative instruments and Hedging Activities
Notional balance				$ 689,059,000
Weighted average interest rate (as a percent)				3.30%
Weighted average capped interest rate (as a percent)				6.50%
Notes Payable Maturities 2027 [Member] | Secured notes
Derivative instruments and Hedging Activities
Number of Real Estate Properties | community		3
Reclassification out of Accumulated Other Comprehensive Income [Member]
Derivative instruments and Hedging Activities
Derivative Instruments, Gain (Loss) Reclassification from Accumulated OCI to Income, Estimated Net Amount to be Transferred				$ 7,012,000